Method and apparatus for positioning a cofferdam

ABSTRACT

A method and apparatus for positioning a cofferdam against a submerged surface. Weights are attached to the cofferdam such that the center of gravity of the cofferdam is closer to the submerged object than the center of gravity of the weights and above the center of gravity of the weights. Lifting eyes are attached to the cofferdam above its center of gravity from which cables extend. The cables support and position the cofferdam. The placement of the weights in relation to the lifting eyes create a moment which maintains contact between the cofferdam and the submerged object.

States Patent Mittleman 1 Nov. 26, 1974 METHOD AND APPARATUS FORPOSITIONING A COFFERDAM [75] Inventor: John R. Mittleman, Arlington,Mass.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

22 Filed: Jan. 2, 1974 21 Appl. No.:430,120

[52] 11.5. C1. 611/68, 114/227 [51] Int. Cl. B63c ll/00, B63c 11/30 [58]Field of Search 61/68, 69; 114/227, 229,

[56] References Cited UNITED STATES PATENTS 7/1902 McLaughlin I 114/2274/1913 Fluceltaub 61/68 Primary Examiner-Jacob Shapiro Attorney, Agent,or Firm-Richard S. Sciascia; Joseph M. St. Amand; Darrell E. Hollis [57]ABSTRACT A method and apparatus for positioning a cofferdam against asubmerged surface. Weights are attached to the cofferdam such that thecenter of gravity of the cofferdam is closer to the submerged objectthan the center of gravity of the weights and above the center ofgravity of the weights. Lifting eyes are attached to the cofferdam aboveits center of gravity from which cables extend. The cables support andposition the cofferdam. The placement of the weights in relation to thelifting eyes create a moment which maintains contact between thecofferdam and the submerged obect.

6 Claims, 4 Drawing Figures PAYENTL IQSVZ Eli-174 METHOD AND APPARATUSFOR POSITIONING A COFFERDAM BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates generally to cofferdams and moreparticularly to cofferdams having weights attached thereto.

2. Description of the Prior Art Once a cofferdam is positioned in thewater and the process of expelling the water from inside the cofferdambegins, the cofferdam becomes buoyant and tremendous forces tend toforce the cofferdam out of the water. These forces must be countered inorder for the cofferdam to maintain its position.

Some prior art devices accomplish this task by bolting or tying thecofferdam to the submerged surface. Such methods require drilling andtapping holes where the structural integrity of the material of thesubmerged surface is questionable. Such an installation requires diverswith special tools and training to perform the underwater operations.Also, there is the ever present danger of the tyings coming loose andattendant danger to workers.

Other prior art devices accomplish the task by driving stakes into thewater bottom and attaching the cof ferdam thereto. This method alsorequires divers and creates an extremely dangerous work environment.

Another prior art device utilizes ballast tanks attached to thecofferdam to accomplish this task. However, due to the size of theballast tank used (the volume of these tanks will be nearly equal to thevolume of the cofferdam itself), a bulky and expensive device iscreated. Accordingly, such devices cannot be utilized in cramped waterspacesa severe limitation. In addition, additional ballast tanks, ifnecessary, must be located above the water level. Since any ballasttanks located above the water must be seaward of the submerged surface,they will create a moment tending to tear the cofferdam away from thesubmerged object-a most undesirable effect, considering the slightnessof wall friction between the cofferdam and the submerged object.

SUMMARY OF THE INVENTION The general purpose of the present invention isto provide a cofferdam that is smaller, easier to maneuver, safer toposition, safer for workmen and is less expen sive than prior artdevices. To attain this, the present invention provides a cofferdamhaving weights attached thereto such that the center of gravity of thecofferdam is closer to the submerged surface than the center of gravityof the weights and above the center of gravity of the weights. Liftingeyes are attached to the cofferdam above its center of gravity fromwhich cables extend. The cables support and position the cofferdam. Theplacement of the weights in relation to the lifting eyes create a momentwhich maintains contact between the cofferdam and the submerged object.

Accordingly, an object of the present invention is to reduce sizewithout reducing effective workspace of a cofferdam.

Another object of the present invention is to increase maneuverabilityof a cofferdam.

Another object of the present invention is to increase safety inpositioning and use of a cofferdam.

Another object of the present invention is to reduce the number ofmanhours as well as the number of workmen required to position acofferdam.

Another object of the present invention is to reduce cost.

Another object of the present invention is to reduce the specializedskills required to position a cofferdam.

Another object of the present invention is to maintain negative buoyancyat all times.

Another object of the present invention is to eliminate diver assistancein positioning a cofferdam.

Another object of the present invention is to mini mize the amount ofsupport equipment needed to position a cofferdam.

Other objects and a more complete appreciation of the present inventionand its many attendant advantages will develop as soon as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingsin which like reference numerals designate like parts throughout thefigures thereof and wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric drawing of aspecific embodiment of the present invention.

FIGS. 2a and 2b are diagrams of the forces and moments of the specificembodiment of FIG. 1.

FIG. 3 illustrates the specific embodiment of FIG. ls placement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT the specific embodimentdescribed, infra, of a cofferdam or water-tight device for makingrepairs below the waterline of a body of water has been developedprimarily for use adjacent steel sheet piling surfaces, such as in FIG.3, for example, although it also may be employed adjacent other surfaceswhere water must be temporarily kept away in order to provide periodicmaintenance thereof.

Referring now to FIGS. 1 and 3, a cofferdam is represented by thenumeral 10. The cofferdam 10 has a floor 12, a rear wall 14, and twoside walls 16. Side walls 16 and floor 12 have edges 18 for abuttingagainst an underwater object to be repaired. It will be appreciated bythose skilled in the art that underwater surfaces have contours to whichedges 18 must conform. Cofferdam 10 is water tight at the junctions offloor 12, rear wall 14 and side walls I6.

It is noted that cofferdam 10 may be made of plywood, aluminum, steel,or other suitable material.

A means for effecting a water-tight seal between edges 18 of cofferdaml0 and the underwater surface is designated by numeral 20. Means 20comprises neoprene, urethane, rubber or other suitable resilientmaterial attached to edges 18.

Attached to and conforming to the contour of cofferdam 10 is frame 22.Frame 22 strengthens cofferdam 10 as well as providing a means forsupporting weights 24. Weights 24 provide cofferdam 10 with a netnegative buoyancy. the center of gravity of weights 24 and frame 10 isbelow the center of gravity of cofferdam l0 and means 20 and ahorizontal distance toward rear wall 14 from the center of gravity ofcofferdam 10 and means 20. It is noted that the center of gravity ofweights 24 and frame 22 may be located, behind the derwater surface thanthe center of gravity of block 42, seaward side of rear wall 14. Weights20 in'the specific sealing pressure P would be a negative value.

embodiment of FIG. 1 are steel plates which, of course, Obviouslynumerous modifications and variations of have a specific gravity ofgreater than one when comthe present invention are possible in light ofthe above pared with the water which is being displaced. 5 teachings. Itis therefore to be understood that within Attached to the top of frame22 are two lifting eyes the scope of the appended claims the inventionmay be 26. Attached to lifting eyes 26 are flexible cables 28. prac i edOtherwise than as specifically described Flexible cables 28 are attachedto means for raising and herein. lowering cofferdam 10 designated bynumeral 30. 1 Claim Frame 22, Lifting eyes 26, and means 30 comprise a10 l. A water-tight device for permitting periodic remeans forsupporting and positioning cofferdam 10, pairs to surfaces below awaterline of a body of water means 20, frame 22 and weights 24. It isnoted that Comprising? means 30 can move cofferdam 10 in threedimensions. a Water-tight cofferdam having a floor, a rear Lifting eyes26 are located above the center of gravity and two side Walls, 531d M$idB Wall f a of cofferdam and means 20. Lifting eyes 20 must be floorhavfng edges for abumng against Said Underlocated a horizontal distancetoward the underwater Water ObJeCt to be repalred;

said cofferdam including means for effecting a water-tight seal betweensaid cofferdam and said submerged object, said means being attached toedges of said two side wall and said floor for abutting against saidunderwater object to be repaired, said cofferdam having a center ofgravity, said rear wall being on one side of said center of gravity andsaid means for effecting a water-tight seal being on the other side ofsaid center of gravity; c. a plurality of weights; d. means forsupporting said weights attached to said cofferdam, said means and saidweights having a center of gravity located a horizontal distance fromsaid center of gravity of said cofferdam in a direction away from thesurface of the underwater object to be repaired and below the center ofgravity of said cofferdam; and

e. means for supporting said cofferdam, said plurality of weights, andsaid means for supporting said surface from the center of gravity offrame 22 and weights 24 for reasons to be discussed, infra.

It is noted that no divers or other underwater personnel are needed toposition cofferdam 10. The requisite amount of weight 24 is connected toframe 22, cofferdam 10 and related parts are lowered into the water,cofferdam 10 is abutted against the underwater surface, and the waterinside cofferdam 10 is expelled. 25

Now turning to FIG. 2a, cofferdam 10 and means 20 are diagrammaticallyillustrated as block 40. Weights 24 and frame 22 are diagrammaticallyillustrated as block 42. Also, shown are lifting eyes 26. FIG. 2aillustrates the forces acting when cofferdam 10 is stationarilypositioned against the underwater surface and the water expelled. ForceL is a lifting force exerted along cables 28. Force R is a reactionforce exertedc on block 40 by the underwater surface. Force W is a forceexerted by the in-water weight of blocks 40 and 42. Angle a is the anglebetween the vertical and cables 28. Dis- Weights attached to the Watertight device above tance D1 is the horizontal distance from lifting eye26 the center of gravity of Said cofferdam and a hori to the center ofgravity of block 42. Distance D2 is the Zontal distance from the centerof grvity of Said vertical distance from lifting eye 26 to floor 12.weight of Said means for pp g Said weights FIG. 2b 18 a schematicrepresentation of the forces L, toward the surface of the underwaterObject to be R, and W of FIG. 2a. repaired From basic mechanics, thefollowing relations are The device of claim 1 wherein Said means fortaken: porting said weights comprises:

L P a w a frame conforming to the contour of said cofferdam L R wherebysaid cofferdam is further strengthened. thus, 3. The device of claim 1wherein said means for sup- R W tan a porting said cofferdam, saidplurality of weights, and also, said means for supporting said weightscomprises:

WDI a. a plurality of lifting eyes attached to said waterthen, so tightdevice;

tan a Dl/D2 b. a plurality of flexible cables, each having a first andthe Pressure holding means 20 against the underwa' a second end, eachsaid first end being attached to ter surface is: one of said pluralityof lifting eyes; and

P 0. means for raising and lowering said device being where, attached tosaid second ends of said plurality of P sealing pressure flexiblecables.

A seal area 4. The device of claim 3 wherein said plurality of lift-Thus, assuming: ing eyes are located in a vertical plane that passes W12,000 lbs. through the center of gravity of said cofferdam.

D1 2 feet 5. A method for positioning a cofferdam for permit- D2 8 feetting periodic repairs to objects below the waterline of A 360 sq. in. abody of water comprising: Then, a. connecting a plurality of weights tosaid cofferdam P =(l2,000 lbs) X (2 ft.)/(8 ft.) X (360 sq. in.) 8 suchthat the center of gravity of said weights is si below the center ofgravity of said cofferdam and It is noted that, if lifting eyes 26 werelocated in a verbetween the center of gravity of said cofferdam andtical plane at further horizontal distance from the unsaid rear wallthereof;

5 6 b. lowering said cofferdam into the water adjacent 6. The method ofclaim 5 wherein said step of consaid underwater object to be repaired;necting comprises:

c. abutting said cofferdam against said underwater a. attaching a meansfor supporting said plurality object to be repaired; v weights to saidcofferdam; and d. effectingawater-tight seal between said cofferdam b.placing said plurality of weights on said support and said underwaterobject to be repaired; and means.

e. expelling the water from inside said cofferdam.

1. A water-tight device for permitting periodic repairs to surfacesbelow a waterline of a body of water comprising: a. a water-tightcofferdam having a floor, a rear wall, and two side walls, said two sidewalls and said floor having edges for abutting against said underwaterobject to be repaired; b. said cofferdam including means for effecting awater-tight seal between said cofferdam and said submerged object, saidmeans being attached to edges of said two side wall and said floor forabutting against said underwater object to be repaired, said cofferdamhaving a center of gravity, said rear wall being on one side of saidcenter of gravity and said means for effecting a water-tight seal beingon the other side of said center of gravity; c. a plurality of weights;d. means for supporting said weights attached to said cofferdam, saidmeans and said weights having a center of gravity located a horizontaldistance from said center of gravity of said cofferdam in a directionaway from the surface of the underwater object to be repaired and belowthe center of gravity of said cofferdam; and e. means for supportingsaid cofferdam, said plurality of weights, and said means for supportingsaid weights attached to the water tight device above the center ofgravity of said cofferdam, and a horizOntal distance from the center ofgravity of said weight and said means for supporting said weights towardthe surface of the underwater object to be repaired.
 2. The device ofclaim 1 wherein said means for supporting said weights comprises: aframe conforming to the contour of said cofferdam whereby said cofferdamis further strengthened.
 3. The device of claim 1 wherein said means forsupporting said cofferdam, said plurality of weights, and said means forsupporting said weights comprises: a. a plurality of lifting eyesattached to said water-tight device; b. a plurality of flexible cables,each having a first and a second end, each said first end being attachedto one of said plurality of lifting eyes; and c. means for raising andlowering said device being attached to said second ends of saidplurality of flexible cables.
 4. The device of claim 3 wherein saidplurality of lifting eyes are located in a vertical plane that passesthrough the center of gravity of said cofferdam.
 5. A method forpositioning a cofferdam for permitting periodic repairs to objects belowthe waterline of a body of water comprising: a. connecting a pluralityof weights to said cofferdam such that the center of gravity of saidweights is below the center of gravity of said cofferdam and between thecenter of gravity of said cofferdam and said rear wall thereof; b.lowering said cofferdam into the water adjacent said underwater objectto be repaired; c. abutting said cofferdam against said underwaterobject to be repaired; d. effecting a water-tight seal between saidcofferdam and said underwater object to be repaired; and e. expellingthe water from inside said cofferdam.
 6. The method of claim 5 whereinsaid step of connecting comprises: a. attaching a means for supportingsaid plurality of weights to said cofferdam; and b. placing saidplurality of weights on said support means.